Techniques have recently been developed for efficiently carrying out the removal of injurious materials such as arsenic, chromium and the like from water containing such materials or the concentration and recovery of beneficial materials such as uranium and the like from water containing such materials, from the view-point of environmental purification or of effective exploitation of resources. Such injurious and beneficial materials exist in water generally as ions and, therefore, it is advantageous that they are separated from water by treatment with an ion exchanger. Particularly, inorganic ion exchangers are, as compared with organic ion exchangers, excellent in stability at a high temperature and under a strong radiation, and have, in most cases, selective ion exchange property for specific ions. Thus, inorganic ion are suitable for the treatment at a high temperature or the treatment of radioactive substances.
In general, it is necessary to form inorganic ion exchangers into a specifically shaped product of a proper size, particularly in the case where the inorganic ion exchangers are used by being packed into a column, in order to lower the resistance to the passage of liquids. In addition, such a shaped product is required to have strength in water, acid resistance and alkali resistance sufficient to withstand an operation such as a back wash, regeneration or the like. In order to form inorganic ion exchangers into a shaped product, known inorganic binders, such as silica sol, water-glass and the like, may be used. However, the shaped products obtained by the use of such inorganic binders are inferior in alkali resistance and have lower ion exchange capacity than that of the ion exchangers prior to being formed into shaped products.
On the other hand, for the forming of inorganic ion exchangers into a shaped product, organic binders such as natural and synthetic polymers may be used. However, the use of an organic binder produces shaped products inferior in heat resistance, acid resistance and alkali resistance. Thus, such shaped products have drawbacks in that they weld together or disintegrate during the treatment at a high temperature or during the regeneration treatment with a strong acid or a strong alkali.
It is the primary object of the present invention to provide an inorganic ion exchanger which has a high ion exchange capacity, is excellent in heat resistance, strength in water, acid resistance and alkali resistance and is useful for the treatment of water containing, as ions, injurious materials or beneficial materials.